Demand Calculations

Hi, I’m just curious if anyone can explain how demand between airports is calculated? I saw that there is a thread that clarifies on this from 2012, but I’m assuming that is out of date.

Basically the demand between two airports is based on real life data of passenger flows. One thing to keep in mind with this model is that airports in the same city can have very different demand since the demand is based on each individual airport passenger flows.